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Zeederbergs Formation

Grid Ref (WGS84 Lat/Long in decimal degrees)

-20.493611, 30.053611
Follow the Railway Road east of the Brest Siding and take the first left turn across the railway line some 500m after the road bends to the north. This track is followed for 2km to just beyond a cattle station. The outcrop is in the Ngezi River, some 500m to the south and downstream
Zederbergs Formation, Ngezi Group

The outcrop shows a pavement of pillow lavas with spherulites, some patches of pillow breccia and a tuff band. The pillows are generally about 1-2m in cross-section and some 3-D exposures suggest lengths of 3-4m. The spherulites tend to be concentrically arranged, with some flow units consisting almost wholly of coalesced spherulites. In some pillows the spherulites appear to be located around cooling cracks.

The feldspars in these rocks are commonly saussuritised but clinopyroxene generally survives. The spherulites consist of radiating aggregates of albite in a dominantly tremolitic matrix.

The geochemistry of these rocks is discussed by Nisbet et al. (1977). They contain about 53.5% SiO2 and 8% MgO. The tuff at this locality penetrates between some of the immediately overlying pillows, but the layer is strongly sheared, a feature of most of the exposed tuffs throughout the belt.

Further Reading: 
Chauvel, C., Dupré, B., Todt, W., Arndt, N.T. and Hofmann, A.W. (1983) Pd and Nd isotopic correlation in Archaean and Proterozoic greenstone belts. Eos (American Geophysical Union Transactions), 64, 330. Hall, R. (1983) B.Sc. Dissertation Project, University of Zimbabwe. Martin, A. (1978) The geology of the Belingwe-Shabani schist belt, Geological Survey of Rhodesia, Bulletin, 83. Nisbet, E.G., Bickle, M.J. and Martin, A. (1977) The mafic and ultramafic lavas of the Belingwe greenstone belt, Rhodesia, Journal of Petrology, 18, 521-66. Orpen, J.L., Bickle, M.J., Nisbet, E.G. and Martin, A. (1985) Belingwe Peak (1:100,000), Geological Survey of Zimbabwe. Scholey, S.P. (1989) M.Phil., Ph.D. Transfer Report, University of Southampton, U.K.
Author Credit: 
Tony Martin